Objectives
Describe how astronomers determine the
composition and surface temperature of a star.
Explain why stars appear to move to an observer on
the earth.
Essential Question
How do astronomers determine the
composition and surface temperature of
a star?
How do stars appear to move to an
observer on the earth?
Chapter 27.1 Vocabulary
Define and give one fact
1.
2.
3.
4.
5.
6.
7.
8.
9.
Star
circumpolar
Red shift
Light years
Parallax
Apparent magnitude
Absolute magnitude
H-R diagram
Main sequence stars
Giants
11. Supergiants
12. White dwarfs
10.
Describe how astronomers
determine the composition
and surface temperature of
a star.
Chapter 27.1 Notes
Describe how astronomers determine the composition and surface temperature of a
star.

Characteristics
of stars




The sun is our closest star
A star is a body of gas that
gives off a tremendous amount
of light and heat
From earth stars look like tiny
white lights, but if you look
closely they shine different
colors (blue, yellow, orange,
red and white)
Stars also vary in mass and
composition
Chapter 27.1 Notes
Describe how astronomers determine the composition and surface temperature of a
star.

Composition
and
temperature



The light of stars is analyzed
through a spectrometer, which
breaks the light into different
wavelengths or colors
The display of colors and lines
is called the spectrum
There are three types of
spectra; emission (bright light),
Absorption (dark line) and
continuous
Chapter 27.1 Notes
Describe how astronomers determine the composition and surface temperature of a
star.

Composition
and
temperature



The dark lines are what tell us
what makes up a star, the
types of materials that can
found in the star
Stars are mainly Hydrogen and
Helium, but also have carbon,
oxygen, nitrogen, and calcium
The temperature range of stars
is 2,800c to 24,000c, with
some blue stars reaching
50,000c
Star
Typ
e
O
B
A
Color
Approximat
e Surface
Temperatur
e
Blue
over 25,000
K
Blue
11,000 25,000 K
Blue
7,500 11,000 K
Averag
e Mass
(The
Sun =
1)
60
18
3.2
Averag
e
Radius
(The
Sun =
1)
15
7
2.5
Average
Luminosit
y (The Sun
= 1)
Main
Characteristic
s
Examples
1,400,000
Singly ionized
helium lines (H
I) either in
emission or
absorption.
Strong UV
continuum.
10
Lacertra
20,000
Neutral helium
lines (H II) in
absorption.
Rigel
Spica
80
Hydrogen (H)
lines strongest
for A0 stars,
decreasing for
other A's.
Sirius,
Vega
6
Ca II
absorption.
Metallic lines
become
noticeable.
Canopus,
Procyon
Sun,
Capella
Arcturus,
Aldebaran
F
Blue
to
White
G
White
to
Yello
w
5,000 - 6,000
K
1.1
1.1
1.2
Absorption
lines of neutral
metallic atoms
and ions (e.g.
once-ionized
calcium).
K
Orang
e to
Red
3,500 - 5,000
K
0.8
0.9
0.4
Metallic lines,
some blue
continuum.
Red
under 3,500
K
0.4
0.04
(very
faint)
M
6,000 - 7,500
K
1.7
0.3
1.3
Some
molecular
bands of
Betelgeuse
,
Explain why stars appear to
move to an observer on the
earth.
Chapter 27.1 Notes
Explain why stars appear to move to an observer on the earth.

Motion




There are two types of motion with
stars apparent and actual
Actual motion can be seen with only
high powered telescopes, because of
the great distances
Apparent motion can be seen every
night as you see stars move across the
sky
Stars also appear to shift as our
seasons change or as we move around
the sun they become visible to us
Chapter 27.1 Notes
Explain why stars appear to move to an observer on the earth.

Motion

Star have three actual motions





First they turn on there axis
Second, most rotate around another star
Third, they move toward or away from earth
There are some stars that seem to
always be out or never drop below the
horizon, these are the circumpolar or the
little dipper
Light has a Doppler effect just like sound


Blue means, it is moving closer to you
Red means, it is moving farther away from
you
Name and describe the way
astronomers measure the
distance from the Earth to
the stars.
Chapter 27.1 Notes
Name and describe the way astronomers measure the distance from the Earth
to the stars.

Star distance is measured in light-years



Light travels at 300,000 km/s or in one year 9.5
trillion miles
The closest star neighbor is Proxima Centauri at
4.2 light years, Sirius the brightest star at night is
9 light years, and Polaris or Northern Star is 700
light years away
Distance is measured using a process known
as parallax


The shift of a star from January to June can be
used to determine distance to within 1,000 light
years
The closer a star is the big the shift
Chapter 27.1 Notes
Name and describe the way astronomers measure the distance from the Earth
to the stars..

Distance
to the
stars

Another method is to use the
brightness of stars – for more distance
stars



They estimate the true brightness by using
the spectrum
They then compare it to its apparent
brightness
Cepheid are stars that pulse in
brightness on a cycle of time


From 1 day to 100 days
The longer the cycle the brighter the star
Chapter 27.1 Notes
Name and describe the way astronomers measure the distance from the Earth
to the stars.

Stellar
Magnitudes
We can see about 6,000 stars with
our eyes
 A good telescope will allow you to
see about 3,000,000,000 (billion)
stars
 The Hubble telescope can see about
1,000,000,000,000 (Trillion) stars
 Stars are broken into two different
skills, how bright they appear from
earth and the other measure is how
bright they would be if all stars were
the same distance

Chapter 27.1 Notes
Explain the difference between absolute magnitude and apparent magnitude.

Apparent
Magnitude

This is how bright a star appears from
earth
Object
mV
Sun
-26.8
Full Moon
-12.5
Venus at brightest
-4.4
Jupiter at brightest
-2.7
Sirius
-1.47
Vega
0.04
Betelgeuse
0.41
Polaris
1.99
Naked eye limit
Pluto
Hubble Space Telescope
6
15.1
31
Chapter 27.1 Notes
Explain the difference between absolute magnitude and apparent magnitude.

Absolute
Magnitude





This is how bright the star would be if it
was 32.6 light years away from the earth
If we take the sun with an apparent
magnitude of -26.8 and moved it 32.6 light
years away, it would have an absolute
magnitude of +5
So if the apparent is less (-26.8) then the
absolute (+5) the star is closer then 32.6
light years
If the apparent is (+6) more then the
absolute (+2) the star is farther then 32.6
light years
3.26 is one parsec – a star that has a
parallax of one second
Chapter 27.1 Notes

Classification
of stars






When you classify stars by there
temperatures and absolute magnitude a
pattern develops
The line through the graph is called the
main sequence of stars, most stars visible
at night are in this group
It starts in the lower right hand corner with
cool, dim and red stars
It then moves up to the upper left corner
with hot, bright, and blue stars
The upper right is cool bright stars
The lower left are hot and dim stars, called
white dwarfs (about the size of earth)
Chapter 27.1 Notes

Classification
of stars
Chapter 27 activity

Procedure
1. Stand directly in front of and directly facing
the red cup at a distance of several meters.
2. Close one eye and sketch the position of the
red cup relative to the background and white
cups.
3. Take several steps back and to the right of
your original position, repeat step 2
4. Take several steps directly back and make
another sketch.
5. Repeat step 4 once again.
Chapter 27 activity - analysis
1.
2.
3.
Compare your drawings. Did the red cup
change position as you viewed it from
different locations? Explain
What kind of results would you expect if
you continued to repeat step 5 at greater
and greater distances? Explain
If you noted the positions of several stars
with a powerful telescope, what would
you expect to observe about their
positions if you sighted the same stars
several months later? Explain
Notes 27.2
Describe how a protostar develops into a
star
 Explain how a main sequence star
generates energy
 Describe the possible evolution of a star
during and after the giant stage

Chapter 27.2 Vocabulary
1.
2.
3.
4.
5.
6.
7.
8.
Nebula
Protostar
Planetary nebula
Novas
Supernova
Neutron star
Pulsars
Black hole
Chapter 27.2 Notes
Describe how a protostar develops into a star

Stellar
Evolution




Nebula – a cloud of gas and dust
Protostar – a shrinking spinning region of gas
that flattens into a disk with a central
concentration
Stars exists for billions of years. Stars form in
nebula that usually are composed of 70%
hydrogen, 28% helium, and 2% heavier
materials.
Gravity pulls it all together. Matter gets warmer
with increased pressure, Over millions years,
until 10,000,000C fusion begins. More than
one star can form, as well as planets
Chapter 27.2 Notes
Explain how a main sequence star generates energy

Main
Sequence
stars




Second and longest stage of a stars life
Energy generated in the core through
fusion of hydrogen into helium, 1g of
hydrogen can generate enough power
to keep a 100 watt bulb burning for
3,000 years.
The energy bubbles upward like boiling
water, gravity prevents the expansion of
the star.
These two forces keep the star at a
stable size, as long as it has enough
hydrogen to convert to helium.
Chapter 27.2 Notes
Describe the possible evolution of a star during and after the giant stage

Giants &
Supergiant




Third stage of a stars life
All atoms of hydrogen have fused into
helium; therefore the core will contract
under the force of gravity.
Temp increases and helium fusion
begins, carbon formed
Hydrogen fusion continues in the areas
surrounding the core and the star
expands into a giant: 10 or more times
larger then our sun, a supergiant is 100
times
Chapter 27.2 Notes
Describe the possible evolution of a star during and after the giant stage

White Dwarf  Planetary nebula – a expanding shell of
Stars
gas left from a dying star.



The end of helium fusion is the end of
the giant stage of a medium size star.
The outer gas layers are lost and the
core revealed, it will heat and illuminate
the expanding gases.
It takes billions of years for a white
dwarf to cool into a black or brown
dwarf, the universe is too young to have
any in it yet.
Chapter 27.2 Notes
Describe the possible evolution of a star during and after the giant stage

Novas



Nova – a white dwarf that explodes as it
cools, becoming a thousand times
brighter for a short time.
Some white dwarfs do not just cool,
they have one or more large
explosions.
Astronomers think this may be caused
by a companion star that is having
material taken from it by the white
dwarf.
Chapter 27.2 Notes
Describe the possible evolution of a star during and after the giant stage

Supernovas




Supernova – a star that explodes with
such tremendous force that it blows
itself apart.
A star with 10 to 100 times of our sun
and the explosions can be 100 times
brighter than novas.
They can release as much energy as
our sun would over 500 million years.
These massive stars continue to fuse
heavier materials until the core turns
into iron, this core then contracts from
gravity and explodes
Chapter 27.2 Notes
Describe the possible evolution of a star during and after the giant stage

Neutron
Stars




Neutron star – an extremely small and
dense ball of neutrons.
Pulsars – two beams of radiation that
sweep across space like a lighthouse
Formed from a supernova, as the star
collapses only neutrons are left. A
spoonful would weigh 100 million tons
on earth
Some give off radiation at the poles
called pulsars, we can detect these as
radio waves.
Chapter 27.2 Notes
Describe the possible evolution of a star during and after the giant stage

Black Holes




Black hole – a hole in space with such
gravity that light can not escape
The most massive stars form black
holes
They are invisible to the eye,
astronomers look for companion stars
that are influenced by the gravity or the
energy of the materials being pulled into
the Black Hole
Massive Black holes may be at the
center of galaxies.
Notes 27.3
Describe the characteristics that identify a
constellation
 Describe the three main types of galaxies
 Explain the big bang theory

Chapter 27.3 Vocabulary
1.
2.
3.
4.
5.
6.
7.
8.
9.
Constellations
Galaxies
Spiral galaxy
Barred spiral galaxy
Elliptical galaxy
Irregular galaxy
Open cluster
Globular clusters
Binary stars
10.
Quasars
Chapter 27.3 Notes
Describe the characteristics that identify a constellation


Star Groups  You see what appear to be single stars,
Constellations




yet only 1 in 4 is actually a single star.
1/3 are double and the rest are triple or
more star groups or clusters.
Constellation – a pattern of stars
There are 88 recognized constellation.
They are used as a star locator map,
the star are labeled by apparent
magnitude and the constellation they
appear in.
Some stars are bright enough to have
been given their own names - Antares
Chapter 27.3 Notes
Describe the three main types of galaxies

Galaxies




Galaxy – A large scale group of stars
The major component of the universe, a
typical galaxy is 100,000 light years in
diameter and has about 100 billion
stars.
Galaxies also contain gas and dust or
nebulae, some are bright because they
reflect light or from the gas within them.
The dark areas absorb light from distant
stars.
Estimates of 50 billion to 1 trillion
galaxies in the known universe.
Chapter 27.3 Notes
Describe the three main types of galaxies

Galaxies



Types of
Galaxies




The two closest to the Milky Way is the
large Magellanic Cloud and the small
Magellanic Cloud at 150,000 light years
There are 17 other galaxies within 3
million light years and this makes up the
Local Group.
Spiral galaxy Barred spiral galaxy Elliptical galaxy Irregular galaxy -
Chapter 27.3 Notes
Describe the three main types of galaxies

The
Milky
Way



Our sun is one of billions stars that
circle the galactic center. It is 2,000
light years thick at the center.
We are 30,000 light years from the
center in a spiral arm.
We revolve around the center at
250km/s, it takes 200 million years to
complete a revolution
Chapter 27.3 Notes
Describe the three main types of galaxies

Star
Cluster




Binary
stars



Open clusters Globular clusters Difference – globular clusters have
more stars, are in the core of the
galaxy and a spherical shape. Open
cluster are a loose grouping and are in
the spiral arms.
Binary stars Used to determine stellar mass
Consist of two stars, a multiple star
system has more then two in orbit
around each other.
Chapter 27.3 Notes
Explain the big bang theory

Formation
of the
Universe





The big bang theory – that the universe
formed from a single point of matter.
Then 12 to 15 billion years ago the “Big
Bang” occurred propelling matter and
energy outward in all directions.
As they moved away from the center
gravity began to have an effect and
formed galaxies
Quasars –
These may be the oldest objects in our
universe
Sun Diagram Page 575